1. Field of the Invention
The present invention relates to a non-aqueous pigment ink.
2. Description of the Related Art
An inkjet recording system is a printing system in which printing is conducted by spraying a liquid ink with a high degree of fluidity from very fine nozzles, and adhering that ink to a recording medium such as a sheet of paper. These systems enable the printing of high-resolution, high-quality images at high speed and with minimal noise, using a comparatively inexpensive printing apparatus, and are rapidly becoming widespread.
The coloring materials for the inks used in these inkjet recording systems can be broadly classified into materials that use pigments and materials that use dyes. Of these, there is a growing tendency for the use of inks that use pigments as the coloring materials, as such inks exhibit the excellent levels of light resistance, weather resistance and water resistance that are required for high image quality printing.
In terms of the solvent, inks can be broadly classified into aqueous inks and non-aqueous inks. Non-aqueous inks that do not use water as the ink solvent, including solvent-based inks that use a volatile solvent as the main constituent and oil-based inks that use a non-volatile solvent as the main constituent, exhibit superior stability within the printer (such as intermittent dischargeability and discharge recovery following standing idle for a long period), cause no curling of the printed paper and have a short ink penetration and drying time, and are therefore attracting considerable attention.
The nozzle plate surface of the print head is often subjected to an ink repellent treatment using a fluorine-based process or the like, but because non-aqueous inks exhibit comparatively high wettability of the nozzle plate surface, the nozzle plate surface tends to be wet relatively easily by the ink. If ink adheres to the nozzle plate surface, then the adhered ink may hinder the discharge of ink droplets. Moreover, the adhered ink may drip onto the paper and soil the printed image.
On the other hand, the print head nozzles used in inkjet printing systems have a very small diameter opening which can sometimes become blocked, and therefore the printing system is usually fitted with a cleaning mechanism. This cleaning is typically conducted by discharging a small amount of ink, suctioning the ink off with a suction device, and then wiping the plate surface with a wiper blade. Abrasion of the nozzle plate surface by the wiper blade tends to cause a deterioration in the ink repellency of the nozzle plate surface.
Patent Document 1 discloses an oil-based ink comprising an ester-based solvent as the solvent, in which by adding a salt of a long-chain polyamide and a polar acid ester in an amount of not less than 1% by mass relative to the total mass of the ink, wetting of the nozzle plate surface by the ink is suppressed. However, in Patent Document 1, no investigation was made regarding deterioration in the ink repellency upon performing cleaning.
Furthermore, in a non-aqueous pigment ink, the pigment tends to penetrate readily, together with the solvent, into the interior of the recording medium, and as a result, the image density tends to deteriorate.
Patent Document 1: Japanese Patent Laid-Open No. 2008-274232